The present invention relates to nonaqueous, microparticle dispersions.
Nonaqueous polyurethane microparticle dispersions have been known in the art for some time. However, the known aqueous polyurethane microparticle dispersions are not without attendant difficulties. The inability to prepare dispersions so that they are uniformly of a small particle size, that is, a predominant number of the particles have a mean diameter on the order of less than five microns, preferably less than one micron has been a major problem. In addition, generally because of the large particle size, nonaqueous polyurethane microparticle dispersions have suffered from the lack of stability especially when the continuous phase is of low viscosity. This typically means that the dispersion either settles upon standing or coagulates and forms large clumps. Moreover, the known nonaqueous polyurethane microparticle dispersions have been typically of low solids content. Therefore their use in coating applications has led to increased volatile organic content of the resultant coating compositions. Efforts to prepare the dispersions at higher solids levels has generally resulted in unmanageably high viscosities. Also, such polyurethane microparticle dispersions typically contain a substantial amount of residual unreacted polyisocyanate monomer which is undesirable from a toxicological standpoint.
In addition, certain compositions are difficult to prepare as nonaqueous dispersions by known techniques. In particular, polyurethane microparticle dispersions where the polyol component is essentially free of arcylic polymer are not available as stable, small particle size nonaqueous dispersions.
There is a need, therefore, for stable nonaqueous polyurethane microparticle dispersions having a uniformly small particle size and which are free of the difficulties attendant upon currently available materials.